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Linux/mm/oom_kill.c

  1 /*
  2  *  linux/mm/oom_kill.c
  3  * 
  4  *  Copyright (C)  1998,2000  Rik van Riel
  5  *      Thanks go out to Claus Fischer for some serious inspiration and
  6  *      for goading me into coding this file...
  7  *  Copyright (C)  2010  Google, Inc.
  8  *      Rewritten by David Rientjes
  9  *
 10  *  The routines in this file are used to kill a process when
 11  *  we're seriously out of memory. This gets called from __alloc_pages()
 12  *  in mm/page_alloc.c when we really run out of memory.
 13  *
 14  *  Since we won't call these routines often (on a well-configured
 15  *  machine) this file will double as a 'coding guide' and a signpost
 16  *  for newbie kernel hackers. It features several pointers to major
 17  *  kernel subsystems and hints as to where to find out what things do.
 18  */
 19 
 20 #include <linux/oom.h>
 21 #include <linux/mm.h>
 22 #include <linux/err.h>
 23 #include <linux/gfp.h>
 24 #include <linux/sched.h>
 25 #include <linux/swap.h>
 26 #include <linux/timex.h>
 27 #include <linux/jiffies.h>
 28 #include <linux/cpuset.h>
 29 #include <linux/export.h>
 30 #include <linux/notifier.h>
 31 #include <linux/memcontrol.h>
 32 #include <linux/mempolicy.h>
 33 #include <linux/security.h>
 34 #include <linux/ptrace.h>
 35 #include <linux/freezer.h>
 36 #include <linux/ftrace.h>
 37 #include <linux/ratelimit.h>
 38 #include <linux/kthread.h>
 39 #include <linux/init.h>
 40 
 41 #include <asm/tlb.h>
 42 #include "internal.h"
 43 
 44 #define CREATE_TRACE_POINTS
 45 #include <trace/events/oom.h>
 46 
 47 int sysctl_panic_on_oom;
 48 int sysctl_oom_kill_allocating_task;
 49 int sysctl_oom_dump_tasks = 1;
 50 
 51 DEFINE_MUTEX(oom_lock);
 52 
 53 #ifdef CONFIG_NUMA
 54 /**
 55  * has_intersects_mems_allowed() - check task eligiblity for kill
 56  * @start: task struct of which task to consider
 57  * @mask: nodemask passed to page allocator for mempolicy ooms
 58  *
 59  * Task eligibility is determined by whether or not a candidate task, @tsk,
 60  * shares the same mempolicy nodes as current if it is bound by such a policy
 61  * and whether or not it has the same set of allowed cpuset nodes.
 62  */
 63 static bool has_intersects_mems_allowed(struct task_struct *start,
 64                                         const nodemask_t *mask)
 65 {
 66         struct task_struct *tsk;
 67         bool ret = false;
 68 
 69         rcu_read_lock();
 70         for_each_thread(start, tsk) {
 71                 if (mask) {
 72                         /*
 73                          * If this is a mempolicy constrained oom, tsk's
 74                          * cpuset is irrelevant.  Only return true if its
 75                          * mempolicy intersects current, otherwise it may be
 76                          * needlessly killed.
 77                          */
 78                         ret = mempolicy_nodemask_intersects(tsk, mask);
 79                 } else {
 80                         /*
 81                          * This is not a mempolicy constrained oom, so only
 82                          * check the mems of tsk's cpuset.
 83                          */
 84                         ret = cpuset_mems_allowed_intersects(current, tsk);
 85                 }
 86                 if (ret)
 87                         break;
 88         }
 89         rcu_read_unlock();
 90 
 91         return ret;
 92 }
 93 #else
 94 static bool has_intersects_mems_allowed(struct task_struct *tsk,
 95                                         const nodemask_t *mask)
 96 {
 97         return true;
 98 }
 99 #endif /* CONFIG_NUMA */
100 
101 /*
102  * The process p may have detached its own ->mm while exiting or through
103  * use_mm(), but one or more of its subthreads may still have a valid
104  * pointer.  Return p, or any of its subthreads with a valid ->mm, with
105  * task_lock() held.
106  */
107 struct task_struct *find_lock_task_mm(struct task_struct *p)
108 {
109         struct task_struct *t;
110 
111         rcu_read_lock();
112 
113         for_each_thread(p, t) {
114                 task_lock(t);
115                 if (likely(t->mm))
116                         goto found;
117                 task_unlock(t);
118         }
119         t = NULL;
120 found:
121         rcu_read_unlock();
122 
123         return t;
124 }
125 
126 /*
127  * order == -1 means the oom kill is required by sysrq, otherwise only
128  * for display purposes.
129  */
130 static inline bool is_sysrq_oom(struct oom_control *oc)
131 {
132         return oc->order == -1;
133 }
134 
135 static inline bool is_memcg_oom(struct oom_control *oc)
136 {
137         return oc->memcg != NULL;
138 }
139 
140 /* return true if the task is not adequate as candidate victim task. */
141 static bool oom_unkillable_task(struct task_struct *p,
142                 struct mem_cgroup *memcg, const nodemask_t *nodemask)
143 {
144         if (is_global_init(p))
145                 return true;
146         if (p->flags & PF_KTHREAD)
147                 return true;
148 
149         /* When mem_cgroup_out_of_memory() and p is not member of the group */
150         if (memcg && !task_in_mem_cgroup(p, memcg))
151                 return true;
152 
153         /* p may not have freeable memory in nodemask */
154         if (!has_intersects_mems_allowed(p, nodemask))
155                 return true;
156 
157         return false;
158 }
159 
160 /**
161  * oom_badness - heuristic function to determine which candidate task to kill
162  * @p: task struct of which task we should calculate
163  * @totalpages: total present RAM allowed for page allocation
164  *
165  * The heuristic for determining which task to kill is made to be as simple and
166  * predictable as possible.  The goal is to return the highest value for the
167  * task consuming the most memory to avoid subsequent oom failures.
168  */
169 unsigned long oom_badness(struct task_struct *p, struct mem_cgroup *memcg,
170                           const nodemask_t *nodemask, unsigned long totalpages)
171 {
172         long points;
173         long adj;
174 
175         if (oom_unkillable_task(p, memcg, nodemask))
176                 return 0;
177 
178         p = find_lock_task_mm(p);
179         if (!p)
180                 return 0;
181 
182         /*
183          * Do not even consider tasks which are explicitly marked oom
184          * unkillable or have been already oom reaped or the are in
185          * the middle of vfork
186          */
187         adj = (long)p->signal->oom_score_adj;
188         if (adj == OOM_SCORE_ADJ_MIN ||
189                         test_bit(MMF_OOM_SKIP, &p->mm->flags) ||
190                         in_vfork(p)) {
191                 task_unlock(p);
192                 return 0;
193         }
194 
195         /*
196          * The baseline for the badness score is the proportion of RAM that each
197          * task's rss, pagetable and swap space use.
198          */
199         points = get_mm_rss(p->mm) + get_mm_counter(p->mm, MM_SWAPENTS) +
200                 atomic_long_read(&p->mm->nr_ptes) + mm_nr_pmds(p->mm);
201         task_unlock(p);
202 
203         /*
204          * Root processes get 3% bonus, just like the __vm_enough_memory()
205          * implementation used by LSMs.
206          */
207         if (has_capability_noaudit(p, CAP_SYS_ADMIN))
208                 points -= (points * 3) / 100;
209 
210         /* Normalize to oom_score_adj units */
211         adj *= totalpages / 1000;
212         points += adj;
213 
214         /*
215          * Never return 0 for an eligible task regardless of the root bonus and
216          * oom_score_adj (oom_score_adj can't be OOM_SCORE_ADJ_MIN here).
217          */
218         return points > 0 ? points : 1;
219 }
220 
221 enum oom_constraint {
222         CONSTRAINT_NONE,
223         CONSTRAINT_CPUSET,
224         CONSTRAINT_MEMORY_POLICY,
225         CONSTRAINT_MEMCG,
226 };
227 
228 /*
229  * Determine the type of allocation constraint.
230  */
231 static enum oom_constraint constrained_alloc(struct oom_control *oc)
232 {
233         struct zone *zone;
234         struct zoneref *z;
235         enum zone_type high_zoneidx = gfp_zone(oc->gfp_mask);
236         bool cpuset_limited = false;
237         int nid;
238 
239         if (is_memcg_oom(oc)) {
240                 oc->totalpages = mem_cgroup_get_limit(oc->memcg) ?: 1;
241                 return CONSTRAINT_MEMCG;
242         }
243 
244         /* Default to all available memory */
245         oc->totalpages = totalram_pages + total_swap_pages;
246 
247         if (!IS_ENABLED(CONFIG_NUMA))
248                 return CONSTRAINT_NONE;
249 
250         if (!oc->zonelist)
251                 return CONSTRAINT_NONE;
252         /*
253          * Reach here only when __GFP_NOFAIL is used. So, we should avoid
254          * to kill current.We have to random task kill in this case.
255          * Hopefully, CONSTRAINT_THISNODE...but no way to handle it, now.
256          */
257         if (oc->gfp_mask & __GFP_THISNODE)
258                 return CONSTRAINT_NONE;
259 
260         /*
261          * This is not a __GFP_THISNODE allocation, so a truncated nodemask in
262          * the page allocator means a mempolicy is in effect.  Cpuset policy
263          * is enforced in get_page_from_freelist().
264          */
265         if (oc->nodemask &&
266             !nodes_subset(node_states[N_MEMORY], *oc->nodemask)) {
267                 oc->totalpages = total_swap_pages;
268                 for_each_node_mask(nid, *oc->nodemask)
269                         oc->totalpages += node_spanned_pages(nid);
270                 return CONSTRAINT_MEMORY_POLICY;
271         }
272 
273         /* Check this allocation failure is caused by cpuset's wall function */
274         for_each_zone_zonelist_nodemask(zone, z, oc->zonelist,
275                         high_zoneidx, oc->nodemask)
276                 if (!cpuset_zone_allowed(zone, oc->gfp_mask))
277                         cpuset_limited = true;
278 
279         if (cpuset_limited) {
280                 oc->totalpages = total_swap_pages;
281                 for_each_node_mask(nid, cpuset_current_mems_allowed)
282                         oc->totalpages += node_spanned_pages(nid);
283                 return CONSTRAINT_CPUSET;
284         }
285         return CONSTRAINT_NONE;
286 }
287 
288 static int oom_evaluate_task(struct task_struct *task, void *arg)
289 {
290         struct oom_control *oc = arg;
291         unsigned long points;
292 
293         if (oom_unkillable_task(task, NULL, oc->nodemask))
294                 goto next;
295 
296         /*
297          * This task already has access to memory reserves and is being killed.
298          * Don't allow any other task to have access to the reserves unless
299          * the task has MMF_OOM_SKIP because chances that it would release
300          * any memory is quite low.
301          */
302         if (!is_sysrq_oom(oc) && tsk_is_oom_victim(task)) {
303                 if (test_bit(MMF_OOM_SKIP, &task->signal->oom_mm->flags))
304                         goto next;
305                 goto abort;
306         }
307 
308         /*
309          * If task is allocating a lot of memory and has been marked to be
310          * killed first if it triggers an oom, then select it.
311          */
312         if (oom_task_origin(task)) {
313                 points = ULONG_MAX;
314                 goto select;
315         }
316 
317         points = oom_badness(task, NULL, oc->nodemask, oc->totalpages);
318         if (!points || points < oc->chosen_points)
319                 goto next;
320 
321         /* Prefer thread group leaders for display purposes */
322         if (points == oc->chosen_points && thread_group_leader(oc->chosen))
323                 goto next;
324 select:
325         if (oc->chosen)
326                 put_task_struct(oc->chosen);
327         get_task_struct(task);
328         oc->chosen = task;
329         oc->chosen_points = points;
330 next:
331         return 0;
332 abort:
333         if (oc->chosen)
334                 put_task_struct(oc->chosen);
335         oc->chosen = (void *)-1UL;
336         return 1;
337 }
338 
339 /*
340  * Simple selection loop. We choose the process with the highest number of
341  * 'points'. In case scan was aborted, oc->chosen is set to -1.
342  */
343 static void select_bad_process(struct oom_control *oc)
344 {
345         if (is_memcg_oom(oc))
346                 mem_cgroup_scan_tasks(oc->memcg, oom_evaluate_task, oc);
347         else {
348                 struct task_struct *p;
349 
350                 rcu_read_lock();
351                 for_each_process(p)
352                         if (oom_evaluate_task(p, oc))
353                                 break;
354                 rcu_read_unlock();
355         }
356 
357         oc->chosen_points = oc->chosen_points * 1000 / oc->totalpages;
358 }
359 
360 /**
361  * dump_tasks - dump current memory state of all system tasks
362  * @memcg: current's memory controller, if constrained
363  * @nodemask: nodemask passed to page allocator for mempolicy ooms
364  *
365  * Dumps the current memory state of all eligible tasks.  Tasks not in the same
366  * memcg, not in the same cpuset, or bound to a disjoint set of mempolicy nodes
367  * are not shown.
368  * State information includes task's pid, uid, tgid, vm size, rss, nr_ptes,
369  * swapents, oom_score_adj value, and name.
370  */
371 static void dump_tasks(struct mem_cgroup *memcg, const nodemask_t *nodemask)
372 {
373         struct task_struct *p;
374         struct task_struct *task;
375 
376         pr_info("[ pid ]   uid  tgid total_vm      rss nr_ptes nr_pmds swapents oom_score_adj name\n");
377         rcu_read_lock();
378         for_each_process(p) {
379                 if (oom_unkillable_task(p, memcg, nodemask))
380                         continue;
381 
382                 task = find_lock_task_mm(p);
383                 if (!task) {
384                         /*
385                          * This is a kthread or all of p's threads have already
386                          * detached their mm's.  There's no need to report
387                          * them; they can't be oom killed anyway.
388                          */
389                         continue;
390                 }
391 
392                 pr_info("[%5d] %5d %5d %8lu %8lu %7ld %7ld %8lu         %5hd %s\n",
393                         task->pid, from_kuid(&init_user_ns, task_uid(task)),
394                         task->tgid, task->mm->total_vm, get_mm_rss(task->mm),
395                         atomic_long_read(&task->mm->nr_ptes),
396                         mm_nr_pmds(task->mm),
397                         get_mm_counter(task->mm, MM_SWAPENTS),
398                         task->signal->oom_score_adj, task->comm);
399                 task_unlock(task);
400         }
401         rcu_read_unlock();
402 }
403 
404 static void dump_header(struct oom_control *oc, struct task_struct *p)
405 {
406         nodemask_t *nm = (oc->nodemask) ? oc->nodemask : &cpuset_current_mems_allowed;
407 
408         pr_warn("%s invoked oom-killer: gfp_mask=%#x(%pGg), nodemask=%*pbl, order=%d, oom_score_adj=%hd\n",
409                 current->comm, oc->gfp_mask, &oc->gfp_mask,
410                 nodemask_pr_args(nm), oc->order,
411                 current->signal->oom_score_adj);
412         if (!IS_ENABLED(CONFIG_COMPACTION) && oc->order)
413                 pr_warn("COMPACTION is disabled!!!\n");
414 
415         cpuset_print_current_mems_allowed();
416         dump_stack();
417         if (oc->memcg)
418                 mem_cgroup_print_oom_info(oc->memcg, p);
419         else
420                 show_mem(SHOW_MEM_FILTER_NODES);
421         if (sysctl_oom_dump_tasks)
422                 dump_tasks(oc->memcg, oc->nodemask);
423 }
424 
425 /*
426  * Number of OOM victims in flight
427  */
428 static atomic_t oom_victims = ATOMIC_INIT(0);
429 static DECLARE_WAIT_QUEUE_HEAD(oom_victims_wait);
430 
431 static bool oom_killer_disabled __read_mostly;
432 
433 #define K(x) ((x) << (PAGE_SHIFT-10))
434 
435 /*
436  * task->mm can be NULL if the task is the exited group leader.  So to
437  * determine whether the task is using a particular mm, we examine all the
438  * task's threads: if one of those is using this mm then this task was also
439  * using it.
440  */
441 bool process_shares_mm(struct task_struct *p, struct mm_struct *mm)
442 {
443         struct task_struct *t;
444 
445         for_each_thread(p, t) {
446                 struct mm_struct *t_mm = READ_ONCE(t->mm);
447                 if (t_mm)
448                         return t_mm == mm;
449         }
450         return false;
451 }
452 
453 
454 #ifdef CONFIG_MMU
455 /*
456  * OOM Reaper kernel thread which tries to reap the memory used by the OOM
457  * victim (if that is possible) to help the OOM killer to move on.
458  */
459 static struct task_struct *oom_reaper_th;
460 static DECLARE_WAIT_QUEUE_HEAD(oom_reaper_wait);
461 static struct task_struct *oom_reaper_list;
462 static DEFINE_SPINLOCK(oom_reaper_lock);
463 
464 static bool __oom_reap_task_mm(struct task_struct *tsk, struct mm_struct *mm)
465 {
466         struct mmu_gather tlb;
467         struct vm_area_struct *vma;
468         struct zap_details details = {.check_swap_entries = true,
469                                       .ignore_dirty = true};
470         bool ret = true;
471 
472         /*
473          * We have to make sure to not race with the victim exit path
474          * and cause premature new oom victim selection:
475          * __oom_reap_task_mm           exit_mm
476          *   mmget_not_zero
477          *                                mmput
478          *                                  atomic_dec_and_test
479          *                                exit_oom_victim
480          *                              [...]
481          *                              out_of_memory
482          *                                select_bad_process
483          *                                  # no TIF_MEMDIE task selects new victim
484          *  unmap_page_range # frees some memory
485          */
486         mutex_lock(&oom_lock);
487 
488         if (!down_read_trylock(&mm->mmap_sem)) {
489                 ret = false;
490                 goto unlock_oom;
491         }
492 
493         /*
494          * increase mm_users only after we know we will reap something so
495          * that the mmput_async is called only when we have reaped something
496          * and delayed __mmput doesn't matter that much
497          */
498         if (!mmget_not_zero(mm)) {
499                 up_read(&mm->mmap_sem);
500                 goto unlock_oom;
501         }
502 
503         /*
504          * Tell all users of get_user/copy_from_user etc... that the content
505          * is no longer stable. No barriers really needed because unmapping
506          * should imply barriers already and the reader would hit a page fault
507          * if it stumbled over a reaped memory.
508          */
509         set_bit(MMF_UNSTABLE, &mm->flags);
510 
511         tlb_gather_mmu(&tlb, mm, 0, -1);
512         for (vma = mm->mmap ; vma; vma = vma->vm_next) {
513                 if (is_vm_hugetlb_page(vma))
514                         continue;
515 
516                 /*
517                  * mlocked VMAs require explicit munlocking before unmap.
518                  * Let's keep it simple here and skip such VMAs.
519                  */
520                 if (vma->vm_flags & VM_LOCKED)
521                         continue;
522 
523                 /*
524                  * Only anonymous pages have a good chance to be dropped
525                  * without additional steps which we cannot afford as we
526                  * are OOM already.
527                  *
528                  * We do not even care about fs backed pages because all
529                  * which are reclaimable have already been reclaimed and
530                  * we do not want to block exit_mmap by keeping mm ref
531                  * count elevated without a good reason.
532                  */
533                 if (vma_is_anonymous(vma) || !(vma->vm_flags & VM_SHARED))
534                         unmap_page_range(&tlb, vma, vma->vm_start, vma->vm_end,
535                                          &details);
536         }
537         tlb_finish_mmu(&tlb, 0, -1);
538         pr_info("oom_reaper: reaped process %d (%s), now anon-rss:%lukB, file-rss:%lukB, shmem-rss:%lukB\n",
539                         task_pid_nr(tsk), tsk->comm,
540                         K(get_mm_counter(mm, MM_ANONPAGES)),
541                         K(get_mm_counter(mm, MM_FILEPAGES)),
542                         K(get_mm_counter(mm, MM_SHMEMPAGES)));
543         up_read(&mm->mmap_sem);
544 
545         /*
546          * Drop our reference but make sure the mmput slow path is called from a
547          * different context because we shouldn't risk we get stuck there and
548          * put the oom_reaper out of the way.
549          */
550         mmput_async(mm);
551 unlock_oom:
552         mutex_unlock(&oom_lock);
553         return ret;
554 }
555 
556 #define MAX_OOM_REAP_RETRIES 10
557 static void oom_reap_task(struct task_struct *tsk)
558 {
559         int attempts = 0;
560         struct mm_struct *mm = tsk->signal->oom_mm;
561 
562         /* Retry the down_read_trylock(mmap_sem) a few times */
563         while (attempts++ < MAX_OOM_REAP_RETRIES && !__oom_reap_task_mm(tsk, mm))
564                 schedule_timeout_idle(HZ/10);
565 
566         if (attempts <= MAX_OOM_REAP_RETRIES)
567                 goto done;
568 
569 
570         pr_info("oom_reaper: unable to reap pid:%d (%s)\n",
571                 task_pid_nr(tsk), tsk->comm);
572         debug_show_all_locks();
573 
574 done:
575         tsk->oom_reaper_list = NULL;
576 
577         /*
578          * Hide this mm from OOM killer because it has been either reaped or
579          * somebody can't call up_write(mmap_sem).
580          */
581         set_bit(MMF_OOM_SKIP, &mm->flags);
582 
583         /* Drop a reference taken by wake_oom_reaper */
584         put_task_struct(tsk);
585 }
586 
587 static int oom_reaper(void *unused)
588 {
589         while (true) {
590                 struct task_struct *tsk = NULL;
591 
592                 wait_event_freezable(oom_reaper_wait, oom_reaper_list != NULL);
593                 spin_lock(&oom_reaper_lock);
594                 if (oom_reaper_list != NULL) {
595                         tsk = oom_reaper_list;
596                         oom_reaper_list = tsk->oom_reaper_list;
597                 }
598                 spin_unlock(&oom_reaper_lock);
599 
600                 if (tsk)
601                         oom_reap_task(tsk);
602         }
603 
604         return 0;
605 }
606 
607 static void wake_oom_reaper(struct task_struct *tsk)
608 {
609         if (!oom_reaper_th)
610                 return;
611 
612         /* tsk is already queued? */
613         if (tsk == oom_reaper_list || tsk->oom_reaper_list)
614                 return;
615 
616         get_task_struct(tsk);
617 
618         spin_lock(&oom_reaper_lock);
619         tsk->oom_reaper_list = oom_reaper_list;
620         oom_reaper_list = tsk;
621         spin_unlock(&oom_reaper_lock);
622         wake_up(&oom_reaper_wait);
623 }
624 
625 static int __init oom_init(void)
626 {
627         oom_reaper_th = kthread_run(oom_reaper, NULL, "oom_reaper");
628         if (IS_ERR(oom_reaper_th)) {
629                 pr_err("Unable to start OOM reaper %ld. Continuing regardless\n",
630                                 PTR_ERR(oom_reaper_th));
631                 oom_reaper_th = NULL;
632         }
633         return 0;
634 }
635 subsys_initcall(oom_init)
636 #else
637 static inline void wake_oom_reaper(struct task_struct *tsk)
638 {
639 }
640 #endif /* CONFIG_MMU */
641 
642 /**
643  * mark_oom_victim - mark the given task as OOM victim
644  * @tsk: task to mark
645  *
646  * Has to be called with oom_lock held and never after
647  * oom has been disabled already.
648  *
649  * tsk->mm has to be non NULL and caller has to guarantee it is stable (either
650  * under task_lock or operate on the current).
651  */
652 static void mark_oom_victim(struct task_struct *tsk)
653 {
654         struct mm_struct *mm = tsk->mm;
655 
656         WARN_ON(oom_killer_disabled);
657         /* OOM killer might race with memcg OOM */
658         if (test_and_set_tsk_thread_flag(tsk, TIF_MEMDIE))
659                 return;
660 
661         /* oom_mm is bound to the signal struct life time. */
662         if (!cmpxchg(&tsk->signal->oom_mm, NULL, mm))
663                 atomic_inc(&tsk->signal->oom_mm->mm_count);
664 
665         /*
666          * Make sure that the task is woken up from uninterruptible sleep
667          * if it is frozen because OOM killer wouldn't be able to free
668          * any memory and livelock. freezing_slow_path will tell the freezer
669          * that TIF_MEMDIE tasks should be ignored.
670          */
671         __thaw_task(tsk);
672         atomic_inc(&oom_victims);
673 }
674 
675 /**
676  * exit_oom_victim - note the exit of an OOM victim
677  */
678 void exit_oom_victim(void)
679 {
680         clear_thread_flag(TIF_MEMDIE);
681 
682         if (!atomic_dec_return(&oom_victims))
683                 wake_up_all(&oom_victims_wait);
684 }
685 
686 /**
687  * oom_killer_enable - enable OOM killer
688  */
689 void oom_killer_enable(void)
690 {
691         oom_killer_disabled = false;
692 }
693 
694 /**
695  * oom_killer_disable - disable OOM killer
696  * @timeout: maximum timeout to wait for oom victims in jiffies
697  *
698  * Forces all page allocations to fail rather than trigger OOM killer.
699  * Will block and wait until all OOM victims are killed or the given
700  * timeout expires.
701  *
702  * The function cannot be called when there are runnable user tasks because
703  * the userspace would see unexpected allocation failures as a result. Any
704  * new usage of this function should be consulted with MM people.
705  *
706  * Returns true if successful and false if the OOM killer cannot be
707  * disabled.
708  */
709 bool oom_killer_disable(signed long timeout)
710 {
711         signed long ret;
712 
713         /*
714          * Make sure to not race with an ongoing OOM killer. Check that the
715          * current is not killed (possibly due to sharing the victim's memory).
716          */
717         if (mutex_lock_killable(&oom_lock))
718                 return false;
719         oom_killer_disabled = true;
720         mutex_unlock(&oom_lock);
721 
722         ret = wait_event_interruptible_timeout(oom_victims_wait,
723                         !atomic_read(&oom_victims), timeout);
724         if (ret <= 0) {
725                 oom_killer_enable();
726                 return false;
727         }
728 
729         return true;
730 }
731 
732 static inline bool __task_will_free_mem(struct task_struct *task)
733 {
734         struct signal_struct *sig = task->signal;
735 
736         /*
737          * A coredumping process may sleep for an extended period in exit_mm(),
738          * so the oom killer cannot assume that the process will promptly exit
739          * and release memory.
740          */
741         if (sig->flags & SIGNAL_GROUP_COREDUMP)
742                 return false;
743 
744         if (sig->flags & SIGNAL_GROUP_EXIT)
745                 return true;
746 
747         if (thread_group_empty(task) && (task->flags & PF_EXITING))
748                 return true;
749 
750         return false;
751 }
752 
753 /*
754  * Checks whether the given task is dying or exiting and likely to
755  * release its address space. This means that all threads and processes
756  * sharing the same mm have to be killed or exiting.
757  * Caller has to make sure that task->mm is stable (hold task_lock or
758  * it operates on the current).
759  */
760 static bool task_will_free_mem(struct task_struct *task)
761 {
762         struct mm_struct *mm = task->mm;
763         struct task_struct *p;
764         bool ret = true;
765 
766         /*
767          * Skip tasks without mm because it might have passed its exit_mm and
768          * exit_oom_victim. oom_reaper could have rescued that but do not rely
769          * on that for now. We can consider find_lock_task_mm in future.
770          */
771         if (!mm)
772                 return false;
773 
774         if (!__task_will_free_mem(task))
775                 return false;
776 
777         /*
778          * This task has already been drained by the oom reaper so there are
779          * only small chances it will free some more
780          */
781         if (test_bit(MMF_OOM_SKIP, &mm->flags))
782                 return false;
783 
784         if (atomic_read(&mm->mm_users) <= 1)
785                 return true;
786 
787         /*
788          * Make sure that all tasks which share the mm with the given tasks
789          * are dying as well to make sure that a) nobody pins its mm and
790          * b) the task is also reapable by the oom reaper.
791          */
792         rcu_read_lock();
793         for_each_process(p) {
794                 if (!process_shares_mm(p, mm))
795                         continue;
796                 if (same_thread_group(task, p))
797                         continue;
798                 ret = __task_will_free_mem(p);
799                 if (!ret)
800                         break;
801         }
802         rcu_read_unlock();
803 
804         return ret;
805 }
806 
807 static void oom_kill_process(struct oom_control *oc, const char *message)
808 {
809         struct task_struct *p = oc->chosen;
810         unsigned int points = oc->chosen_points;
811         struct task_struct *victim = p;
812         struct task_struct *child;
813         struct task_struct *t;
814         struct mm_struct *mm;
815         unsigned int victim_points = 0;
816         static DEFINE_RATELIMIT_STATE(oom_rs, DEFAULT_RATELIMIT_INTERVAL,
817                                               DEFAULT_RATELIMIT_BURST);
818         bool can_oom_reap = true;
819 
820         /*
821          * If the task is already exiting, don't alarm the sysadmin or kill
822          * its children or threads, just set TIF_MEMDIE so it can die quickly
823          */
824         task_lock(p);
825         if (task_will_free_mem(p)) {
826                 mark_oom_victim(p);
827                 wake_oom_reaper(p);
828                 task_unlock(p);
829                 put_task_struct(p);
830                 return;
831         }
832         task_unlock(p);
833 
834         if (__ratelimit(&oom_rs))
835                 dump_header(oc, p);
836 
837         pr_err("%s: Kill process %d (%s) score %u or sacrifice child\n",
838                 message, task_pid_nr(p), p->comm, points);
839 
840         /*
841          * If any of p's children has a different mm and is eligible for kill,
842          * the one with the highest oom_badness() score is sacrificed for its
843          * parent.  This attempts to lose the minimal amount of work done while
844          * still freeing memory.
845          */
846         read_lock(&tasklist_lock);
847         for_each_thread(p, t) {
848                 list_for_each_entry(child, &t->children, sibling) {
849                         unsigned int child_points;
850 
851                         if (process_shares_mm(child, p->mm))
852                                 continue;
853                         /*
854                          * oom_badness() returns 0 if the thread is unkillable
855                          */
856                         child_points = oom_badness(child,
857                                 oc->memcg, oc->nodemask, oc->totalpages);
858                         if (child_points > victim_points) {
859                                 put_task_struct(victim);
860                                 victim = child;
861                                 victim_points = child_points;
862                                 get_task_struct(victim);
863                         }
864                 }
865         }
866         read_unlock(&tasklist_lock);
867 
868         p = find_lock_task_mm(victim);
869         if (!p) {
870                 put_task_struct(victim);
871                 return;
872         } else if (victim != p) {
873                 get_task_struct(p);
874                 put_task_struct(victim);
875                 victim = p;
876         }
877 
878         /* Get a reference to safely compare mm after task_unlock(victim) */
879         mm = victim->mm;
880         atomic_inc(&mm->mm_count);
881         /*
882          * We should send SIGKILL before setting TIF_MEMDIE in order to prevent
883          * the OOM victim from depleting the memory reserves from the user
884          * space under its control.
885          */
886         do_send_sig_info(SIGKILL, SEND_SIG_FORCED, victim, true);
887         mark_oom_victim(victim);
888         pr_err("Killed process %d (%s) total-vm:%lukB, anon-rss:%lukB, file-rss:%lukB, shmem-rss:%lukB\n",
889                 task_pid_nr(victim), victim->comm, K(victim->mm->total_vm),
890                 K(get_mm_counter(victim->mm, MM_ANONPAGES)),
891                 K(get_mm_counter(victim->mm, MM_FILEPAGES)),
892                 K(get_mm_counter(victim->mm, MM_SHMEMPAGES)));
893         task_unlock(victim);
894 
895         /*
896          * Kill all user processes sharing victim->mm in other thread groups, if
897          * any.  They don't get access to memory reserves, though, to avoid
898          * depletion of all memory.  This prevents mm->mmap_sem livelock when an
899          * oom killed thread cannot exit because it requires the semaphore and
900          * its contended by another thread trying to allocate memory itself.
901          * That thread will now get access to memory reserves since it has a
902          * pending fatal signal.
903          */
904         rcu_read_lock();
905         for_each_process(p) {
906                 if (!process_shares_mm(p, mm))
907                         continue;
908                 if (same_thread_group(p, victim))
909                         continue;
910                 if (is_global_init(p)) {
911                         can_oom_reap = false;
912                         set_bit(MMF_OOM_SKIP, &mm->flags);
913                         pr_info("oom killer %d (%s) has mm pinned by %d (%s)\n",
914                                         task_pid_nr(victim), victim->comm,
915                                         task_pid_nr(p), p->comm);
916                         continue;
917                 }
918                 /*
919                  * No use_mm() user needs to read from the userspace so we are
920                  * ok to reap it.
921                  */
922                 if (unlikely(p->flags & PF_KTHREAD))
923                         continue;
924                 do_send_sig_info(SIGKILL, SEND_SIG_FORCED, p, true);
925         }
926         rcu_read_unlock();
927 
928         if (can_oom_reap)
929                 wake_oom_reaper(victim);
930 
931         mmdrop(mm);
932         put_task_struct(victim);
933 }
934 #undef K
935 
936 /*
937  * Determines whether the kernel must panic because of the panic_on_oom sysctl.
938  */
939 static void check_panic_on_oom(struct oom_control *oc,
940                                enum oom_constraint constraint)
941 {
942         if (likely(!sysctl_panic_on_oom))
943                 return;
944         if (sysctl_panic_on_oom != 2) {
945                 /*
946                  * panic_on_oom == 1 only affects CONSTRAINT_NONE, the kernel
947                  * does not panic for cpuset, mempolicy, or memcg allocation
948                  * failures.
949                  */
950                 if (constraint != CONSTRAINT_NONE)
951                         return;
952         }
953         /* Do not panic for oom kills triggered by sysrq */
954         if (is_sysrq_oom(oc))
955                 return;
956         dump_header(oc, NULL);
957         panic("Out of memory: %s panic_on_oom is enabled\n",
958                 sysctl_panic_on_oom == 2 ? "compulsory" : "system-wide");
959 }
960 
961 static BLOCKING_NOTIFIER_HEAD(oom_notify_list);
962 
963 int register_oom_notifier(struct notifier_block *nb)
964 {
965         return blocking_notifier_chain_register(&oom_notify_list, nb);
966 }
967 EXPORT_SYMBOL_GPL(register_oom_notifier);
968 
969 int unregister_oom_notifier(struct notifier_block *nb)
970 {
971         return blocking_notifier_chain_unregister(&oom_notify_list, nb);
972 }
973 EXPORT_SYMBOL_GPL(unregister_oom_notifier);
974 
975 /**
976  * out_of_memory - kill the "best" process when we run out of memory
977  * @oc: pointer to struct oom_control
978  *
979  * If we run out of memory, we have the choice between either
980  * killing a random task (bad), letting the system crash (worse)
981  * OR try to be smart about which process to kill. Note that we
982  * don't have to be perfect here, we just have to be good.
983  */
984 bool out_of_memory(struct oom_control *oc)
985 {
986         unsigned long freed = 0;
987         enum oom_constraint constraint = CONSTRAINT_NONE;
988 
989         if (oom_killer_disabled)
990                 return false;
991 
992         if (!is_memcg_oom(oc)) {
993                 blocking_notifier_call_chain(&oom_notify_list, 0, &freed);
994                 if (freed > 0)
995                         /* Got some memory back in the last second. */
996                         return true;
997         }
998 
999         /*
1000          * If current has a pending SIGKILL or is exiting, then automatically
1001          * select it.  The goal is to allow it to allocate so that it may
1002          * quickly exit and free its memory.
1003          */
1004         if (task_will_free_mem(current)) {
1005                 mark_oom_victim(current);
1006                 wake_oom_reaper(current);
1007                 return true;
1008         }
1009 
1010         /*
1011          * The OOM killer does not compensate for IO-less reclaim.
1012          * pagefault_out_of_memory lost its gfp context so we have to
1013          * make sure exclude 0 mask - all other users should have at least
1014          * ___GFP_DIRECT_RECLAIM to get here.
1015          */
1016         if (oc->gfp_mask && !(oc->gfp_mask & (__GFP_FS|__GFP_NOFAIL)))
1017                 return true;
1018 
1019         /*
1020          * Check if there were limitations on the allocation (only relevant for
1021          * NUMA and memcg) that may require different handling.
1022          */
1023         constraint = constrained_alloc(oc);
1024         if (constraint != CONSTRAINT_MEMORY_POLICY)
1025                 oc->nodemask = NULL;
1026         check_panic_on_oom(oc, constraint);
1027 
1028         if (!is_memcg_oom(oc) && sysctl_oom_kill_allocating_task &&
1029             current->mm && !oom_unkillable_task(current, NULL, oc->nodemask) &&
1030             current->signal->oom_score_adj != OOM_SCORE_ADJ_MIN) {
1031                 get_task_struct(current);
1032                 oc->chosen = current;
1033                 oom_kill_process(oc, "Out of memory (oom_kill_allocating_task)");
1034                 return true;
1035         }
1036 
1037         select_bad_process(oc);
1038         /* Found nothing?!?! Either we hang forever, or we panic. */
1039         if (!oc->chosen && !is_sysrq_oom(oc) && !is_memcg_oom(oc)) {
1040                 dump_header(oc, NULL);
1041                 panic("Out of memory and no killable processes...\n");
1042         }
1043         if (oc->chosen && oc->chosen != (void *)-1UL) {
1044                 oom_kill_process(oc, !is_memcg_oom(oc) ? "Out of memory" :
1045                                  "Memory cgroup out of memory");
1046                 /*
1047                  * Give the killed process a good chance to exit before trying
1048                  * to allocate memory again.
1049                  */
1050                 schedule_timeout_killable(1);
1051         }
1052         return !!oc->chosen;
1053 }
1054 
1055 /*
1056  * The pagefault handler calls here because it is out of memory, so kill a
1057  * memory-hogging task. If oom_lock is held by somebody else, a parallel oom
1058  * killing is already in progress so do nothing.
1059  */
1060 void pagefault_out_of_memory(void)
1061 {
1062         struct oom_control oc = {
1063                 .zonelist = NULL,
1064                 .nodemask = NULL,
1065                 .memcg = NULL,
1066                 .gfp_mask = 0,
1067                 .order = 0,
1068         };
1069 
1070         if (mem_cgroup_oom_synchronize(true))
1071                 return;
1072 
1073         if (!mutex_trylock(&oom_lock))
1074                 return;
1075         out_of_memory(&oc);
1076         mutex_unlock(&oom_lock);
1077 }
1078 

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